Permeability properties and structural failure mechanism of laminated sandstone under fluid–solid coupling considering excavation unloading effect

The significant joints, high in-situ stress—osmotic pressure coupling and excavation disturbances were prone to cause deep surrounding rock to undergo continuous excavation processes. It included the crack-initiation, -propagation, -nucleation, rib-spalling and roof-falling, collapse and instability, disaster appearing, corresponding to the disaster -incubation, -induction, -causation and -manifestation. The evolution processes restricted the coal mining efficiency. Therefore, the fluid–solid coupling mechanical tests considering the effects of confining pressures, excavation and bedding were conducted. Then, the permeability properties were characterized. The macroscopic- and microscopic- structural characteristics were clarified. Meanwhile, the fractal and chaotic characteristics of fracture structures were obtained. Subsequently, the structural failure mechanism was revealed. The research results were as follows: (1) The bedding played a significant driving role in the development, expansion and formation of the microscopic pore-cracks structures; (2) The higher the effective confining pressure was, the more complex the distribution characteristics of molecular fracture structures was, and the more significant the chaotic characteristics was; (3) Due to the effects of bedding buckling, water wedging, seepage water lubrication, tensile-shear combined and shear sliding friction, different bedding angles result in different macroscopic—microscopic—molecular structural failure mechanisms. These research results could help improve the prevention accuracy of underground disasters in coal mining.